Optionally compile wasmtime-bench-api with wasi-nn and wasi-crypto (#2677)

This adds the ability to add feature flags (e.g. `--features wasi-nn`) when compiling `wasmtime-bench-api` to allow benchmarking Wasmtime with WASI proposals included. Note that due to https://github.com/rust-lang/cargo/issues/5364, these features are only available:
 - in the `crates/bench-api` directory, e.g. `pushd crates/bench-api; cargo build --features wasi-crypto`
 - or from the top-level project directory using `-Zpackage-features`, e.g. `OPENVINO_INSTALL_DIR=/opt/intel/openvino cargo +nightly build -p wasmtime-bench-api -Zpackage-features --features wasi-nn`

Cargo.lock

@@ -3148,6 +3148,8 @@ dependencies = [
  "wasi-cap-std-sync",
  "wasmtime",
  "wasmtime-wasi",
+ "wasmtime-wasi-crypto",
+ "wasmtime-wasi-nn",
  "wat",
 ]